The present invention relates to a cover plate for an electric motor having a brush array and interference suppression devices.
Traditional cover plates consist of synthetic material and act as chassis for the brush array of the electric motor, which has, for example, carbon brushes and carbon holders to locate the carbon brushes. Normally, interference suppression devices, such as coils or capacitors for example, are also mounted directly on the cover plate.
A great disadvantage of known cover plates is that they are designed only for a temperature range of up to a maximum of about 120xc2x0 C. Since known systems do not provide for any monitoring of the cover plate temperature, it is not possible to fully exploit the output potential of the electric motor without the risk of exceeding the maximum permissible temperature for the cover plate.
A further disadvantage of known systems is that electronic components for evaluating motor speed and the like are mounted on a separate board, which has to be connected to the cover plate in an additional production step during manufacture.
The object of the present invention is to create an improved cover plate for an electric motor by avoiding the disadvantages of the prior art just detailed and thus to provide an improved electric motor.
In the case of a cover plate for an electric motor with a brush array, this object is achieved under the invention by mounting additional electronic components directly on and/or integrating them into the cover plate. This simplifies the manufacturing process in particular.
A particularly advantageous aspect of the present invention is characterized in that electrical conductors which make contact with the brush array and/or the interference suppression devices are mounted directly on the cover plate and/or are integrated into the cover plate, whereby a separate connection of the brush array or the interference suppression devices to each other, or with additional electrical components using wires as required, is no longer necessary.
Interference suppression devices can be attached to the cover plate using hollow rivets which are welded to the connections of the interference suppression devices and are connected in an electrically conductive manner to the corresponding electrical conductors of the cover plate.
It is also advantageous to position electrical conductors to make contact with the additional electrical components directly on the cover plate, so that no plug or wire connections are needed to connect the additional electrical components.
It is also conceivable to integrate at least parts of the electrical conductors into a injection-molded circuit board.
A particularly advantageous aspect of the present invention is characterized in that at least one encoder to determine the speed of the electric motor is mounted directly on the cover plate. The encoder or encoders is/are preferably configured as Hall effect generators.
It is also very advantageous to mount two encoders on the cover plate. With a particular alignment of the two encoders relative to each other and to a magnetized trigger wheel connected to the armature shaft of the electric motor, it is possible to determine the direction of rotation of the electric motor from a phase shift of the output signals from the two encoders.
Because of the common arrangement of the encoders on the cover plate there is only minimal assembly expense involved in mounting the encoders in the correct position relative to the trigger wheel.
Another advantageous aspect of the cover plate under the invention is characterized in that a diagnostic circuit is mounted directly on the cover plate. In a particularly advantageous version, the diagnostic circuit has at least one preferably ohmic voltage divider, where a first node of the voltage divider is connected to a first reference potential in the diagnostic circuit, and a second node of the voltage divider is connected to a second reference potential in the diagnostic circuit.
Preferably the voltage divider consists of three ohmic resistors connected in series. Each of the two outer nodes of the voltage divider is connected to different reference potentials in the diagnostic circuit, so that the difference between the two reference potentials drops over the voltage divider.
A signal output of an encoder is connected to a third node of the voltage divider, and finally a signal line is connected to a fourth node of the voltage divider, so that, depending on the potential at the signal output of the encoders, different potentials are present at the fourth node of the voltage divider and thus at the signal line.
This circuitry makes it possible to detect short circuits in the signal output from the encoder, and other components, to the reference potential of the supply voltage of the additional electronic components and to the ground reference potential. Faulty wiring during manufacture or short circuits which only become apparent during operation can be detected easily, by evaluating the signal from the signal line.
A further, quite particularly advantageous aspect of the cover plate of the invention is characterized in that a temperature sensor is mounted directly on the cover plate, which makes it possible to measure the temperature of the cover plate during operation. Operating reliability and the life of the electric motor are substantially increased by monitoring the temperature of the cover plate in this way. For example, depending on a signal from the temperature sensor, it is possible to activate the electric motor directly, or to turn it off when a pre-set maximum temperature for the cover plate is exceeded, or to operate it at reduced output.